The invention relates to an extruder having a transfer region which, in an extruder sleeve, has ribs between which extend flow channels, whereby opposite the sleeve flow channels, flow channels are formed in the extruder screw, and whereby the sum of the cross-sections of the flows channels, when viewed in the direction of extrusion, shift toward the sleeve and then toward the screw.
Such an extruder is known, for example, from AT-E-40073B. It has a transfer region in which the material that is to be extruded is pressed out of the region of the extruder screw into threads provided in the extruder sleeve. By the transfer from the extruder screw into the region of the extruder sleeve, and back, the mixing of the starting materials is to be improved, which represents an important qualify feature of the extruded material. To avoid losses, the cross-sectional areas of the flow channels are precisely coordinated, and the extruder screw runs exactly in the extruder sleeve, with the exception of the structurally required gap of, for example, 100 μm in conformity with the bearing play and the bending of the extruder screw during the rotation and stress.
It has also been proposed to change the flow cross-section in a defined manner in order to generate shear flows that are intended to improve the mixing. By reducing the cross-sectional surface there results, with rubber mixtures, which to this extent act like Newton's liquids, an elongated flow that corresponds to an acceleration of the mixture in an axially parallel direction of the extruder. However, this unfortunately results in a reduction of the retention time of the extruded material in the extruder. The discontinuous pitch in the screw lands of the transfer mixture region to this extent reduces the homogenization; the temperature behavior also becomes worse. The discontinuous pitch is therefore only well suited for rubber mixtures that are easy to process.
In contrast, it is an object of the invention to provide an extruder, the temperature distribution and homogenization capability of which are improved even with exacting mixtures such as natural rubber.